Arrange the sliced potato and onion in layers in a greased baking dish, sprinkling each layer with oil (a total of 3 tablespoons), garlic, salt, and pepper.
Scatter the tomato wedges over the potatoes, cover tightly with foil, and bake for some 45 minutes to an hour or so, or until the potatoes are almost tender.
Meanwhile, sprinkle the fish steaks on both sides with a little salt and let sit.
Place the fish over the potatoes, brush the fish with remaining 1 tablespoon oil, sprinkle thyme, rosemary, oregano, parsley, and lemon juice over the fish and potatoes. Pour in the wine and sprinkle the top with breadcrumbs.
Return to the oven, and cook until the fish is just done, about 15 minutes, basting several times.
You can use any firm-fleshed white fish for this recipe, such as rosada, turbot, halibut, tilapia, cod, etc.